SANTA CLARA -- Right tackle Anthony Davis returned to the 49ers’ 90-man roster on Saturday, but the roster spot that opened is a huge loss for the team.

The 49ers placed nose tackle Ian Williams on the reserve/non-football injury list, a season-ending move. Williams sustained an ankle injury and underwent surgery in the offseason.

The 49ers originally agreed to a five-year contract extension with Williams in the offseason. However, the contract was amended to a one-year deal after he underwent a team physical after undergoing surgery on his left leg.

It is not known how Williams sustained the non-football injury in the offseason.

The move to place Williams on the season-ending list opens a roster spot for Davis’ return from the reserve/retired list. Davis, the 49ers’ No. 11 overall selection in the 2010 draft, started all 71 games in which he appears in his five seasons.

Davis stepped away from the game last June to let his mind and body heal, he said. Davis had an injury plagued 2014 season that limited him to seven games. After missing time with shoulder, knee, ankle and hamstring issues, Davis sat out four games late in the season with a concussion.